Treatment of CBA mice with goldthioglucose (GTG) induces selective damage to the ventral medial hypothalamic nuclei within hours. The nature of the injury and cause for its specificity are still controversial. The arcuate nucleus. the most ventral of the hypothalamic nuclei, in untreated animals has the general characteristics of typical central nervous tissue. The extracellular space is relatively small and the capillaries are closely surrounded by astrocyte processes and contain an endothelium that is nonfenestrated and joined by tight junctions. For this proposed study, light/electron microscopy and intravascu- lar injected tracers will be used to study the blood-brain carrier in mice at the level of the arcuate nucleus. The study will include untreated animals, animals treated with goldthioglucose, and animals with angiotension-induced acute hypertension.